I here have become a grammarian, I who never learned any language but by rote, and who do not yet know adjective, conjunction, or ablative.  I think I have read that the Romans had a sort of horses by them called ‘funales’ or ‘dextrarios’, which were either led horses, or horses laid on at several stages to be taken fresh upon occasion, and thence it is that we call our horses of service ‘destriers’; and our romances commonly use the phrase of ‘adestrer’ for ‘accompagner’, to accompany.  They also called those that were trained in such sort, that running full speed, side by side, without bridle or saddle, the Roman gentlemen, armed at all pieces, would shift and throw themselves from one to the other, ‘desultorios equos’.  The Numidian men-at-arms had always a led horse in one hand, besides that they rode upon, to change in the heat of battle: 

“Quibus, desultorum in modum, binos trahentibus equos, inter acerrimam saepe pugnam, in recentem equum, ex fesso, armatis transultare mos erat:  tanta velocitas ipsis, tamque docile equorum genus.”

     ["To whom it was a custom, leading along two horses, often in the
     hottest fight, to leap armed from a tired horse to a fresh one; so
     active were the men, and the horses so docile.”—­Livy, xxiii. 29.]

There are many horses trained to help their riders so as to run upon any one, that appears with a drawn sword, to fall both with mouth and heels upon any that front or oppose them:  but it often happens that they do more harm to their friends than to their enemies; and, moreover, you cannot loose them from their hold, to reduce them again into order, when they are once engaged and grappled, by which means you remain at the mercy of their quarrel.  It happened very ill to Artybius, general of the Persian army, fighting, man to man, with Onesilus, king of Salamis, to be mounted upon a horse trained after this manner, it being the occasion of his death, the squire of Onesilus cleaving the horse down with a scythe betwixt the shoulders as it was reared up upon his master.  And what the Italians report, that in the battle of Fornova, the horse of Charles viii., with kicks and plunges, disengaged his master from the enemy that pressed upon him, without which he had been slain, sounds like a very great chance, if it be true.

[In the narrative which Philip de Commines has given of this battle, in which he himself was present (lib. viii. ch. 6), he tells us of wonderful performances by the horse on which the king was mounted.  The name of the horse was Savoy, and it was the most beautiful horse he had ever seen.  During the battle the king was personally attacked, when he had nobody near him but a valet de chambre, a little fellow, and not well armed.  “The king,” says Commines, “had the best horse under him in the world, and therefore he stood his ground bravely, till a number of his men, not a great way from him, arrived at the critical minute.”]